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<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
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<body>
    <input type="text" id="username">
    <script>
         //表单事件：失去焦点事件blur
         $("#username").blur(function(){
            console.log("失去焦点");
        $("usename").val("");
         })
    </script>
</body>

</html>